What symbols/characters are not allowed in tags?

3 Answers 3


What characters are allowed in tag names?

Always allowed

  • lowercase Latin letters a to z
  • digits 0 to 9

Conditionally allowed

Related Questions


On the sidebar it says that these are the Tag Characters:

Tag characters: [a-z 0-9 + # - .]

I'd assume anything not listed there is invalid.

  • Do you know what happens when you assume? Sep 18, 2009 at 17:25
  • 1
    You get struck by lightning?
    – Randell
    Sep 18, 2009 at 17:26
  • 14
    You split assume into an array by substring index 0,3 3,1 4,2 Sep 18, 2009 at 17:29
  • It's worth noting that + is only allowed at the end of a tag name.
    – Stevoisiak
    Jul 20, 2017 at 2:12

At least for chat room tags I was just able to create a tag español for the Spanish chat room. I thought the system would automatically change it to espanol like it does for the question tags. So I went further and tried to create a 日本語 for the Japanese chat room, but it got converted to ???.

So the answer may be:

  • Some Latin-1 characters are no longer disallowed


  • That subsets of characters not allowed in question tags is different to that not allowed in chat room tags


  • There's a bug in chat room tags that allows you to use characters that are not supposed to be allowed

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